WO2000023694A2

WO2000023694A2 - Method for reducing nitrogen oxide in the exhaust gases of an internal combustion engine operated with a lean mixture

Info

Publication number: WO2000023694A2
Application number: PCT/EP1999/007213
Authority: WO
Inventors: Ekkehard Pott; Gunnar Splisteser
Original assignee: Volkswagen Aktiengesellschaft
Priority date: 1998-10-16
Filing date: 1999-09-29
Publication date: 2000-04-27
Also published as: CN1330745A; EP1121513A2; WO2000023694A3; DE19847874A1; EP1121513B1; CN1131929C; DE59901151D1

Abstract

The invention relates to a method for reducing nitrogen oxide in the exhaust gases of an internal combustion engine operating with a lean mixture and having a downstream NOx accumulation catalyst, wherein NOx accumulation is favored by measures aimed at increasing exhaust gas temperature and/or decreasing mass flow rate and NOx regeneration of the catalyst is controlled in such a way that optimal exhaust gas purification is achieved. In order to control NOx regeneration, the charging state of the catalyst with nitrogen oxide is determined and/or catalyst activity is monitored by means of an onboard diagnosis system. If maximum acceptable charging is surpassed or irregularities in catalyst activity are encountered, reliability of NOx regeneration is initially verified by checking whether safety-relevant components are functioning properly and/or whether the actual driving situation complies with predetermined driving parameters. A test is also carried out to determine whether it is possible to carry out NOx regeneration by complying with predetermined regeneration parameters. If reliability requirements are met, the necessary regeneration parameters are optionally regulated and NOx regeneration is initiated and carried out until a predetermined degree of regeneration is achieved or the results of the reliability tests show that the regeneration process should be aborted or interrupted. In this case, NOx regeneration is resumed depending on the degree of regeneration already achieved once reliability requirements are met or the process is repeated by returning to the above-mentioned step of the process in a similar way as when the regeneration process is normally ended. In view of the fact that the inventive method is particularly suitable for common rail diesel engines, the invention also describes a common rail diesel engine for the implementation of the inventive method that comprises a corresponding exhaust gas purification device.

Description

Process for nitrogen oxide reduction in the exhaust gas of a lean-fueled

Internal combustion engine

The present invention relates to a method for reducing nitrogen oxide in the exhaust gas of a lean-burn internal combustion engine with a downstream NO _x storage or NOx storage catalytic converter. In particular, it relates to a method for optimally controlling the NO _x regeneration of the NO _x storage catalytic converter and a method for improving nitrogen oxide storage. It also relates to a common rail diesel engine for carrying out the method with an associated exhaust gas cleaning device.

NOx storage catalytic converters consist of a conventional 3-way coating, which is expanded by a NO _x storage component. They store nitrogen oxides through the formation of nitrate in the lean exhaust gas and convert them into harmless N ₂ under reducing conditions in the rich exhaust gas, whereby they are specifically emptied in order to essentially retain their full absorption capacity for nitrogen oxides, which decreases continuously with increasing nitrogen oxide loading in the lean phase.

To minimize nitrogen oxide emissions, it is therefore necessary to store the nitrogen oxides in the catalyst as effectively as possible and to regenerate the loaded catalyst in a timely and effective manner by intermittently lowering the lambda value into the rich operating range.

Particular problems arise with diesel engines, since they usually do not run with λ <1. This type of internal combustion engine therefore requires special motor measures (such as throttling without a drop in torque) for NO _x regeneration, which can lead to an undesirable change in driving behavior. Moreover, in typical diesel exhaust temperatures below 200 ° C, a NO _x regeneration is not possible. Besides, there is only one inadequate NO _x storage. In addition, high exhaust gas mass flows also cause problems with NO _x storage efficiency.

In order to reduce nitrogen oxide in the exhaust gas of a lean-burn internal combustion engine, a control method for the NO _x regeneration of an associated NO _x storage catalytic converter is described in German patent application 197 16275.4. In this method, the loading state of the catalytic converter is first determined and compared with a predetermined threshold value. If this value is exceeded, it is checked whether the operating conditions and the driving situation permit NO _x regeneration. If this is the case, the necessary regeneration is initiated, while otherwise it is waited until the operating conditions and the driving situation allow it or until a second threshold value for the nitrogen oxide loading of the catalytic converter is exceeded. Regeneration is then initiated by deliberately changing the operating conditions and carried out until the loading state of the catalytic converter falls below the first threshold value. However, if the driving situation does not allow this, regeneration is not initiated or regeneration that has already started is terminated prematurely to ensure that no dangerous operating situations can occur. An aborted regeneration process will only be resumed if, due to the current driving situation, there are no longer any concerns about the implementation of such a measure. Measures to improve NO _x storage are not apparent from the patent application mentioned.

The object of the present invention is to provide a method for reducing nitrogen oxide in the exhaust gas of a lean-burn internal combustion engine with a downstream NO _x storage catalytic converter, which enables the most effective storage of the released nitrogen oxides in the catalytic converter as well as by improving the described NO _x regeneration process a catalyst activity that is always sufficiently high for proper functioning of the catalytic converter is ensured without this resulting in a noticeable change in the operating behavior of the internal combustion engine or even in dangerous driving situations. The object is also to create a common rail diesel engine with an associated exhaust gas purification device for carrying out this method. According to the invention, the NO _x storage and the storage effectiveness are improved by measures that increase the exhaust gas temperature and / or reduce the mass flow. In particular, in the low-load range, partial throttling takes place via a throttle valve, a small amount of post-injection additionally being able to contribute to increasing the catalyst temperature. At higher loads, a boost pressure reduction as well as a change in the EGR rate or the exhaust gas recirculation rate and / or a variation in the start of injection / the injection duration of the pre-injection, main injection and post-injection quantity can also be used. By maintaining a minimum temperature of around 190-200 ° C in the NO _x storage catalyst flow, the possibilities for carrying out a NO _x regeneration are also significantly expanded.

In the NO _x regeneration process according to the invention, the loading state of the NO _x storage catalytic converter with nitrogen oxides is determined in a first process step (process step a) and compared with a predetermined maximum permissible nitrogen oxide load corresponding to a just allowed minimum catalytic activity in order to determine the optimal time for carrying out a regeneration to investigate.

In order to determine an irregularity in the catalyst activity, an OBD check (OBD = on-board diagnosis) of the NO _x storage catalyst is also carried out (method step b.).

If an irregularity is found or if the permissible catalyst load is exceeded, the admissibility of a NO _x regeneration is first checked in order to avoid undesirable or even dangerous operating conditions or driving situations. Here, safety-relevant components are checked for proper functioning and / or the current driving situation for compliance with predetermined driving parameters (method step c).

Simultaneously with the admissibility check or afterwards, a check is carried out in a further method step (method step d) to determine whether there is currently a possibility of carrying out a NOx regeneration by adhering to predetermined regeneration parameters. This check can also take place before the admissibility check. If necessary, the required regeneration parameters are set and the regeneration is initiated. Otherwise, process step c.) Is repeated until NO _x regeneration is permissible. If necessary, a detected malfunction of one of the safety-relevant components that hinders regeneration is also displayed.

Storing catalyst finally regenerated in a last method step e) until a predetermined degree of regeneration - if the NOx regeneration is both permitted as possible of the NO _x.. Subsequently, the normal operating conditions are set again and there is a return to step a.).

If the current results of the admissibility check of procedural step c.), Which also persists when performing procedural steps d.) And e.), This will result in a premature termination or at least an interruption of the NO _x regeneration and a return to the recognized inadmissibility of the regeneration process Process step a.) Or c). If applicable, a detected malfunction of one of the safety-relevant components is also displayed.

The decision about a return to method step a.) Or a return to method step c.) Is preferably made on the basis of the degree of regeneration currently achieved, which is compared with a predetermined degree of regeneration. If this value is undershot, ie if a corresponding nitrogen oxide loading level is exceeded, the catalytic converter is not functioning properly and the regeneration process is initiated by returning to the admissibility check of process step c.). If, on the other hand, the predetermined degree of regeneration is reached or exceeded, a sufficiently high catalytic activity is already ensured _by falling below a critical nitrogen oxide load and the process step a.) Is returned to the determination of the optimal time for the next NO _x regeneration. The degree of NO _x regeneration achieved is determined via the state of loading of the catalyst with nitrogen oxides. In a preferred method variant, the necessary regeneration parameters are set in method step d.) Only after a predetermined first time period and / or after at least a second threshold value for the nitrogen oxide loading has been exceeded, in order to have to intervene as little as possible in the operating behavior of the internal combustion engine.

Further preferred process variants can be found in the associated subclaims.

In order to be able to use the method with a common rail diesel engine, this is additionally provided according to the invention with a throttle valve arranged in front of the intake manifold.

An exhaust gas purification device for carrying out the method according to the invention comprises a NOx storage catalytic converter, to which the optimum NO _x regeneration temperature is at least one temperature sensor connected upstream or downstream, from whose measured values the actually desired catalyst temperature is determined. The NO _x storage catalyst can also preceded by a broadband lambda probe for determining the lambda value and an NO _x - be connected downstream of the sensor for determining the NO _x emission.

Further features and advantages of the method according to the invention and the devices mentioned for carrying out this method result not only from the associated claims — individually and / or in combination — but also from the following description of preferred exemplary embodiments in conjunction with the associated drawings. The drawings show:

Fig. 1 is a flowchart of the NO _x regeneration method according to the invention and

FIG. 2 shows a schematic illustration of a common rail diesel engine with a downstream exhaust gas cleaning device for carrying out the method according to FIG. 1. The starting point for the method according to the invention is the continuous determination of the NO _x storage activity or the NO _x emission slip, which, in the case of lean operation, is based on the current loading state of the NO _x storage catalytic converter, the inflowing NO _x raw emission, the exhaust gas or catalyst temperature and the exhaust gas mass flow The raw NO _x emission is determined here on the basis of a map from the consumption or from the engine operating points driven (speed n, current injection quantity M_E). It can be corrected via correction fields for the boost pressure, the EGR rate, the throttle valve position as well as the start of the pre-injection and main injection and the duration of the pre-injection.

Since the catalytic activity and thus the functionality of the catalytic converter, as already mentioned, gradually decreases with increasing nitrogen oxide loading, one is required to ensure proper functioning of the catalytic converter if a maximum permissible nitrogen oxide loading or a predetermined threshold value corresponding to a minimum permissible catalytic activity is undershot NO _x regeneration is considered necessary and the measures required for this are taken in the form of the method steps described below.

To ensure proper operation of the NO _x storage catalytic converter, in addition to the determination of the loading condition, an OBD check (OBD = on-board diagnosis) of the catalytic converter takes place, which essentially consists of monitoring the NO _x storage activity to determine any occurrences There are irregularities. The nominal values of the NO _x storage efficiency therefore serve as an input signal for the OBD control.

Irregularities in the catalyst activity are essentially noticeable through two damage patterns, which can also occur together:

■ After NO _x regeneration, good NO _x storage is measured first, but the saturation sets in faster and more strongly than calculated.

■ After a NOx regeneration, a stronger NO _x breakthrough is measured than is to be expected according to calculations. If the precious metal components of the catalyst are occupied or destroyed, in addition to the decreasing NO _x activity, a reduction in the HC \ CO ^" and particle conversion must also be expected, so that a comparison of the calculated and the measured NO _x storage efficiency is sufficient for catalyst diagnosis. Irregularities in the catalyst activity are therefore determined by determining NO _x breakthroughs which must exceed a predetermined threshold value in a predetermined time window of approximately 30 s, which, up to a raw NO _x emission of approximately 10 g / h, a deviation of approximately 2 g / h between the actual value and corresponds to the target value, while for higher NO _x raw emissions it corresponds to a deviation of 20%.

After such an irregularity in the catalyst activity has been determined, at least one advanced NO _x regeneration is carried out first by carrying out the method steps described below. If the irregularities persist, at least de-sulfation is additionally initiated, as is the case when the sulfur load is too high.

To carry out an advanced or regular NO _x regeneration, the current driving situation is first checked for compliance with predetermined driving parameters, since such a measure is not permissible in all driving or operating situations. In particular, the speed, the load, the load change and the driving speed must be within the specified permissible limits, which must be observed so that NO _x regeneration can take place or a regeneration process that has already started is not interrupted or interrupted.

At very high speeds or loads, the exhaust gas mass flow, which is very high especially in turbo engines, can be enriched to a lambda value of less than 1, as is required to carry out NO _x regeneration, only in conjunction with high exothermic energy in the exhaust gas, so that no regeneration takes place at speeds of more than approximately 3600 min ^"1. Even at speeds of less than approximately 1200 min ^{" 1} , NO _x regeneration is suppressed, since this should only take place during driving at correspondingly high speeds in order to avoid acoustic influences to shift the required partial throttling in driving phases with higher rolling and wind noise, ie higher speeds, and to avoid any undesirable, odor-intensive reaction products that may occur when the vehicle is at a standstill or closed to emit low driving speed. For this reason, the permissible minimum speed for performing NO _x regeneration is limited to approximately 20 km / h.

To avoid dangerous driving situations, NO _x regeneration is not permitted even if the load changes suddenly. A measure of the load change requests is a change in time of the pedal value transmitter PWG or the PWG speed, which, for example, must not exceed a value of approximately 100% / s.

The permissibility of a NO _x regeneration in a given driving situation can also be derived from threshold values for the injection quantity, the speed gradient or for a thrust detection or braking signal, the injection quantity, for example, being 10-90% of the maximum value depending on the engine type used. If one or more of these options are not required, they can be taken out of operation by appropriate selection of the threshold values or admissibility limits or by software or hardware switches.

The NO _x storage catalytic converter always requires a cooling or recovery pause until a renewed regeneration, the duration of which depends on the time, after a de-sulfation or a completely progressing or for the reasons explained below, interrupted or prematurely terminated NO _x regeneration The preparation time and the actual regeneration time required to reach the regeneration state. Typical times are between 30 and 300 s, but in particular between 40 and 60 s. After completion of a NO _x regeneration, a time function is started by a corresponding abort or end signal, which calculates a variable recovery time depending on the preparation and regeneration time, in which no NO _x regeneration is permitted. Before initiating regeneration, compliance with the required recovery period is therefore checked as a further requirement for admissibility.

Since the required enrichment of the exhaust gas flow to λ <1 leads to an increase in the total amount of fuel injected and thus to an increase in output MISSING UPON TIME OF PUBLICATION

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An additional control is carried out via a lambda signal which, in order to ensure a sufficiently rapid oxidation reaction on the pre-catalytic converter and the NO _x storage catalytic converter, must not fall below a predetermined lower threshold value which corresponds to the lambda value to be set by engine measures during NO _x regeneration.

Depending on the lambda value before the motor measures are initiated, the preparation of the NO _x regeneration can first be carried out by motor measures, such as, for example, B. a partial throttling of the internal combustion engine and / or an increase in the EGR rate and / or a reduction in the boost pressure (taking into account the particle emission and correction of the main injection quantity to compensate for any power drops as a result of the throttling), can be initiated quickly. With the approach of a predetermined lambda threshold value of approximately 1.1-1.6, in particular, however, approximately 1.3-1.5, the adjustment speed of the actuators is then increasingly slowed down in order to enable the main injection to be adapted almost torque-neutral. This lambda value depends on the operating point of the engine and can be dynamically corrected using the PWG speed.

After completion of this first stage, the post-injection quantity is ramped up in a second stage and its maximum value is regulated in such a way that the lambda value after the engine is the value of the regeneration lambda value of approximately 0.75-0.99, but in particular approximately 0 , 92 - 0.99. The injection point is set so that the post-injection takes place in the expansion stroke after the end of combustion or in the exhaust stroke. If the post-injection takes place during the end of combustion, this energy output must be compensated for by correcting the main injection quantity. The value of the regeneration lambda value can vary over the regeneration time depending on the state of loading of the catalytic converter with nitrogen oxides and sulfur, the exhaust gas flow and the exhaust gas temperature before and after the NO _x storage catalytic converter.

Since the NO _x regeneration mainly takes place with CO as the regeneration agent, the pre-injection quantity is increased in a third stage depending on the operating point and damped to a value of about 1 - 50%, but in particular 5 - 20%, of the main injection quantity and at the same time the main injection quantity is dependent on the operating point and withdrawn subdued. The pre-injection time is before the start of ignition in the intake stroke or in the first phase of the compression stroke.

In order to influence the driving behavior as little as possible, the setting of the required regeneration parameters can also only take place after a predetermined period of time has elapsed or after a second threshold value for nitrogen oxide loading has been exceeded, which, for example, corresponds to a loading in which regeneration is urgently required. In this case, the loading state of the NO _x storage catalytic converter is divided by the threshold values into three characteristic areas in which "regeneration is not necessary", "regeneration is necessary" or "regeneration is urgently necessary". It is also a combination of both methods or a finer subdivision of the loading condition by using further threshold values.

In the "regeneration required" state, NO _x regeneration of the NO _x storage catalytic converter then only takes place if the operating situation permits regeneration, ie if the specified admissibility requirements are met and the required operating parameters are set and enable regeneration. Otherwise, regeneration is waited until the "regeneration urgently needed" state is reached. Then, however, when the admissibility requirements are met, various motor measures of the type mentioned, which are carried out individually or in combination, influence the operating parameters in such a way that regeneration can take place. The operating behavior of the internal combustion engine is influenced as little as possible by this two-stage procedure known from the aforementioned German patent application 197 16275.4.

Before the NO _x regeneration begins, the residual oxygen stored in the NO _x storage catalytic converter must first be consumed. The excess of reducing agent that can be used with rich exhaust gas can be calculated from the HC and CO mass flow. The stored nitrogen oxides are then reacted with the excess of reducing agent. The reaction is not completely stoichiometric, but is corrected via the lambda value, the exhaust gas mass flow and the exhaust gas temperature before and after the NO _x storage catalytic converter. The actual NO _x regeneration is achieved by partially throttling the engine, and / or increasing the EGR rate, and / or lowering the boost pressure (taking into account the particle emission), and / or increasing the pre- and post-injection quantity and / or controlled a reduction in the main injection quantity.

In particular due to the partial throttling, a change in torque is to be expected, which must be corrected by adapting the main injection quantity without the driver noticing a change in driving behavior. In this case, the change in torque can also be corrected only after a certain threshold value has been exceeded.

To correct this, a setpoint torque is first called up using a map. Torque changes as a result of an engine intervention result from deviations in the gas exchange work and through combustion carry-over as a result of other throttle valve and EGR and boost pressure settings. In addition, incomplete combustion at very low lambda values as a result of throttling / boost pressure reduction / increase in the EGR rate leads to a correction of the target torque. With very high post-injection quantities, fuel residues remain in the cylinder, which only burn in the next cycle and are therefore also torque-influencing. Finally, in order to facilitate the application, a further correction field is added to determine the actual torque.

A change in the main injection quantity is only released when a predetermined threshold value of the torque deviation is exceeded.

The absolute discharge of the NO _x storage catalytic converter possible per unit of time in the rich exhaust gas depends on the available reducing agent supply, ie on the available reducing agent amount and the

Reducing agent composition in fat. The regeneration process is also influenced by the loading condition of the catalyst, the NO _x and residual oxygen content of the incoming exhaust gas, the temperature of the storage catalyst, the exhaust gas mass flow and the O ₂ storage capacity of the washcoat and can be modeled. The CO and HC mass flows in the exhaust gas can be omitted Calculate the start of injection and the duration of the pre-injection, main injection and post-injection as well as the speed and the air mass flow.

The NO _x regeneration is usually carried out until a predetermined degree of regeneration is reached. Then normal operating conditions are set again and the determination of the loading condition described at the beginning is started again in order to determine the time for the next NO _x regeneration.

This regular termination of the NO _x regeneration is carried out in the reverse order of the NO _x regeneration. First, the pre-injection quantity is ramped back to the normal value in a time-controlled manner, but the rate of change is greater than when the regeneration is carried out. The post-injection can be stopped at the same time without delay, since it has no or at most a minor influence on the combustion process. In addition, the throttle valve, the EGR controller and the boost pressure controller are based on the lambda value and the operating point (speed n, current injection quantity M_E). dependent adjustment speed returned to the normal values.

In some cases, however, a regeneration process that has already started may be terminated prematurely or at least interrupted if the regeneration process is inadmissible due to the current results of the admissibility check already described.

If a NO _x regeneration is terminated prematurely, the main and pre-injection quantities are immediately set to the normal value and the post-injection is switched off at the same time. However, if the termination of the regeneration process results from a driving speed that is too low, ie a speed of less than approximately 20 km / h, the post-injection is only reduced for a certain cycle time. The post-injection is not switched off if the termination of the NO _x regeneration is due to an excessive change in load, ie if the time change of the pedal value transmitter PWG exceeds a predetermined threshold value. Depending on the calculated or measured lambda value, the throttle valve, the EGR controller and the boost pressure regulator are returned to normal at high speed. Another possibility for a sudden inadmissibility of the NO _x regeneration process consists in an excessive thermal load on the NO _x storage catalytic converter by exceeding a threshold value for the total regeneration time, which results from the preparatory or necessary to switch from the normal operating state to the regeneration state Heating time and the actual regeneration time required to carry out a regeneration. Alternatively, threshold values for the individual times can also be used. The permissible regeneration time here is approximately a maximum of 5-30 s, but in particular approximately 15 s.

After the premature termination or interruption of the regeneration process, the permissibility of a regeneration and the possibility of carrying it out are continuously checked in order, if necessary, to terminate the aborted regeneration process by continuing as soon as possible, and thus the full functionality of the NO _x - To be able to restore storage catalyst.

In addition, the nitrogen oxide loading of the NO _x storage catalytic converter and hence its degree of regeneration is determined and compared with a maximum permissible residual loading of about 5 - determined based 15% on the loading condition at the initiation of NO _x regeneration. If this value is undershot, the NO _x storage catalytic converter has already been regenerated sufficiently well by the preceding regeneration process to be able to ensure proper functioning. In this case, the regeneration process is finally stopped and the time for the next regular NO _x regeneration is determined by returning to the continuous determination of the loading state described at the beginning.

If, on the other hand, the specified residual load is reached or exceeded, the interrupted regeneration process is continued after the admissibility requirements have been met again until the predetermined degree of regeneration has been reached. In order to be able to use the energy used to heat the storage catalytic converter as optimally as possible, the catalytic converter temperature is maintained here by weakened temperature-maintaining measures and only after a predetermined time period of approximately 10-300 s, in particular, however 30 - 50 s, reduced to normal operating values without meeting the admissibility requirements.

The NO _x regeneration is considered to have ended when the deviation of the actual lambda value from the normal lambda value lies below a certain threshold value, the lambda value being determined both by measurement using a lambda sensor and by calculation can be.

In order to ensure proper functioning of the NO _x storage catalytic converter, the number of NO _x regenerations carried out subsequently is determined after a premature NO _x regeneration and / or desulfation based on an irregularity in the catalytic activity determined by the OBD control and a predetermined one Minimum number of consecutive NO _x regenerations compared, which is 10-100, but preferably about 20. If a new irregularity in the catalyst activity occurs before this minimum number is reached, a catalyst defect is assumed, which is indicated by an appealing display device.

Between the individual regeneration processes, the NO _x storage in the storage catalytic converter is promoted by measures that increase the exhaust gas temperature and reduce the exhaust gas mass flow, which leads to a noticeable reduction in nitrogen oxide emissions compared to conventional exhaust gas purification processes. The improvement in NO _x storage takes place in particular by increasing the exhaust gas temperature upstream of the NO _x storage catalytic converter to a value of more than about 190 ° C. by means of an EGR change, throttling the amount of fresh air by up to 70% and reducing the boost pressure up to towards pure suction operation. These values are corrected via the exhaust gas temperature and the PWG dynamics. The measures are inserted and ground out in a dampened manner. Since the catalysts are still too cold to convert pollutants at these temperatures, post-injection makes no sense. Only thermal measures may be taken.

Fig. 2 shows a schematic representation of a for carrying out the regeneration process of the invention and improve the NO _x - storage, that is, for effectively reducing the emission of nitrogen oxides suitable common rail diesel engine 10 with an upstream suction tube 12 and a therein built-in throttle valve 14, which is arranged behind charge pressure and temperature sensors (not shown) but in front of an EGR inlet 16 and serves to reduce the air-fuel ratio lambda without torque drops. The throttle valve 14 is controlled either by a pulse width modulated signal with a fixed frequency, which results from the duty cycle of the control, or by a CAN message which describes the position of the throttle valve 14 as a percentage. The idle position of the throttle valve 14 is basically in the “open” position. The definition of which value of the control signal corresponds to which throttle valve position can be set by software.

The exhaust gas of the diesel engine 10 passes through an exhaust gas line 18 with an exhaust gas turbocharger 20 into an exhaust gas cleaning device with a pre-catalytic converter 22 and a NO _x storage catalytic converter 24. The pre-catalytic converter 22 is preceded by a broadband lambda probe 26 for measuring the lambda value, which additionally or alternatively The lambda value is calculated.

A temperature sensor 28 or 30 for monitoring the minimum or maximum permissible regeneration temperature is arranged in front of the NO _x storage catalytic converter 24 and after the NO _x storage catalytic converter 24. The temperature sensors 28, 30 also serve to monitor what is required for de-sulfation

Temperature range and to control the optimal NO _x storage by temperature-increasing measures. The catalytic activity of the NO _x storage catalytic converter 24 can be monitored by comparing the outlet temperature of the exhaust gas flowing out of the NO _x storage catalytic converter 24 with the inlet temperature of the exhaust gas flowing into the catalytic converter 24.

The NOx storage catalyst 24 is a _NOx sensor 38 downstream for measurement of the nitrogen oxide emissions, which serves for the determination of irregularities in catalyst activity.

The measurement signals of the broadband lambda probe 26, the temperature sensors 28, 30 and the NO _x sensor 38 are applied via lines 32, 34, 40 to an associated control device 36 for controlling the motor 10.

Claims

PATENT CLAIMS

1. Method for NO _x regeneration of a NO _x storage catalytic converter (24) connected downstream of a lean-burn internal combustion engine (10), with the following method steps:

a) determining the loading state of the NO _x storage catalytic converter (24) with nitrogen oxides and comparing the determined loading values with a predetermined first threshold value for a maximum permissible nitrogen oxide loading and / or

b.) OBD control of the NO _x storage catalyst (24) for monitoring the catalyst activity;

c.) If the threshold value is exceeded or if an irregularity in the catalyst activity is determined, checking the permissibility of a NO _x regeneration by checking the correct functioning of safety-relevant components and / or checking the current driving situation for compliance with predetermined driving parameters;

d.) Checking whether the maintenance of predetermined regeneration parameters provides the possibility of carrying out a NO _x regeneration, possibly setting the required NO _x regeneration parameters and initiating the NO _x regeneration if such a measure is permissible, otherwise repeating the method step c.) and / or, if appropriate, signaling a detected malfunction of one of the safety-relevant components; and e.) Carrying out the NO _x regeneration until a predetermined NO _x regeneration degree has been reached, setting normal operating conditions and returning to method step a.) or prematurely terminating or interrupting the NO _x regeneration if the current results of the admissibility check of method step c .) this requires returning to method step a.) or c.) and / or possibly signaling a detected malfunction of one of the safety-relevant components.

2. The method according to claim 1, characterized in that the setting of the required regeneration parameters in method step d.) Takes place only after a predetermined first time period and / or after exceeding at least a second threshold value for the nitrogen oxide loading.

3. The method according to claim 1 or 2, characterized in that after a premature termination or interruption of the NO _x regeneration, the loading state of the NO _x storage catalytic converter (24) with nitrogen oxides is determined and if a predetermined degree of regeneration is undershot, ie if a predetermined level is exceeded Nitrogen oxide loading, a return to NO _x regeneration is initiated by returning to method step c.), While returning to method step a.) Takes place when the predetermined degree of regeneration is reached or exceeded.

4. The method according to claim 3, characterized in that the predetermined degree of regeneration is less than 5 - 15% residual load based on the loading state when initiation of NO _x regeneration.

5. The method according to any one of the preceding claims, characterized in that a common rail diesel engine is used as the internal combustion engine (10).

6. The method according to any one of the preceding claims, characterized in that the injection system and / or the throttle valve (14) and / or the EGR / boost pressure controller are checked as safety-relevant components.

7. The method according to any one of the preceding claims, characterized in that the driving situation is derived from a threshold value for the pedal value transmitter PWG and / or the injection quantity and / or the speed and / or a thrust detection signal and / or a brake signal and / or a speed gradient.

8. The method according to any one of the preceding claims, characterized in that a NO _x regeneration is carried out only when a certain minimum speed is exceeded.

9. The method according to claim 8, characterized in that the

The minimum speed is 20 km / h.

10. The method according to any one of the preceding claims, characterized in that a NO _x regeneration is carried out only in a certain speed or load range and in a certain range of load change requests or the PWG speed.

11. The method according to claim 10, characterized in that the speed range 1200 - 3600 min ^"1 , while the maximum PWG speed is <100% / s.

12. The method according to any one of the preceding claims, characterized in that a NO _x regeneration is only carried out when the main injection quantity is 10 - 90% of the maximum value.

13. The method according to any one of the preceding claims, characterized in that compliance with the required regeneration temperature is monitored by determining the exhaust gas temperature before and / or after the NO _x storage catalyst (24).

14. The method according to any one of the preceding claims, characterized in that an exhaust gas temperature of 220-500 ° C is set to carry out a NO _x regeneration.

15. The method according to any one of the preceding claims, characterized in that the exhaust gas or catalyst temperature by adjusting the EGR rate and / or a throttle valve and / or the boost pressure regulator, and / or the post-injection quantity and / or the time of the post-injection and / or the start of injection of the main injection is controlled.

16. The method according to any one of the preceding claims, characterized in that the preparation time required to set the regeneration state and the regeneration time required to carry out a NO _x regeneration are determined and that the NO _x regeneration after exceeding a predetermined maximum allowable preparation time and / or Regeneration period is interrupted or terminated prematurely.

17. The method according to claim 16, characterized in that the maximum permissible regeneration time is 5 - 30 s.

18. The method according to claim 17, characterized in that the maximum permissible regeneration time is 15 s.

19. The method according to any one of the preceding claims, characterized in that no renewed NO _x regeneration or desulfation is carried out within a predetermined minimum recovery time after a proper termination or a premature termination or interruption of a NO _x regeneration.

20. The method according to claim 19, characterized in that the minimum recovery time is variable depending on the preparation time required to set the regeneration state and the actual regeneration duration.

21. The method according to claim 19 or 20, characterized in that the minimum recovery time is 30-300 s.

22. The method according to claim 21, characterized in that the minimum recovery time is 40-60 s.

23. The method according to any one of the preceding claims, characterized in that the catalyst temperature is maintained after an interruption or a premature termination of the NO _x regeneration by weakened temperature-preserving measures and is only reduced to normal operating values after a predetermined second period of time.

24. The method according to claim 23, characterized in that the predetermined second time period is 10-300 s.

25. The method according to claim 24, characterized in that the predetermined second time period is 30 - 50 s.

26. The method according to any one of the preceding claims, characterized in that the NO _x storage activity or the NO _x emission slip in lean operation based on the current loading state of the NOx storage catalyst (24), the outflowing NO _x raw emissions, the exhaust gas or Catalyst temperature and the exhaust gas mass flow is determined.

27. The method according to claim 26, characterized in that the NO _x - raw emission is determined on the basis of a map from the consumption or the engine operating points driven (speed n, current injection quantity M_E).

28. The method according to claim 27, characterized in that the determined NO _x - raw emission values are corrected via correction fields for the boost pressure, the EGR rate, the throttle valve position and the start of the pre-injection and main injection and the duration of the pre-injection.

29. The method according to any one of the preceding claims, characterized in that the NO _x regeneration by partial throttling of the internal combustion engine (10) and / or increasing the EGR rate and / or lowering the boost pressure and / or Raising the pre-injection and / or post-injection quantity and / or lowering the main injection quantity is controlled.

30. The method according to claim 29, characterized in that the lambda value in a first stage by partial throttling of the internal combustion engine (10) and / or increasing the EGR rate and / or lowering the boost pressure is first lowered to a predetermined first lambda threshold and is then set in a second stage by controlling the post-injection to the final regeneration lambda value.

31. The method according to claim 30, characterized in that the predetermined lambda threshold is 1, 1 - 1, 6.

32. The method according to claim 31, characterized in that the predetermined lambda threshold value is 1, 3 - 1, 5.

33. The method according to any one of claims 30 to 32, characterized in that the predetermined regeneration lambda value is 0.75 to 0.99.

34. The method according to claim 33, characterized in that the regeneration lambda value is 0.92 - 0.99.

35. The method according to claim 30, characterized in that the pre-injection quantity is increased in a third stage to 1-50% of the main injection quantity.

36. The method according to claim 35, characterized in that the pre-injection quantity is increased to 5 - 20% of the main injection quantity.

37. The method according to any one of the preceding claims, characterized in that occurring torque changes are corrected by controlling the main injection quantity.

38. The method according to claim 37, characterized in that the

Torque changes can only be corrected after a certain threshold value has been exceeded.

39. The method according to any one of the preceding claims, characterized in that irregularities in the catalyst activity with regard to all pollutants are determined by determining NO _x breakthroughs.

40. The method according to claim 39, characterized in that the NO _x breakthroughs have to exceed a certain threshold value in a certain time window.

41. The method according to claim 40, characterized in that the threshold value must be exceeded for more than 30 s.

42. The method according to claim 40 or 41, characterized in that the threshold value corresponds to a raw NO _x emission of 10 g / h a deviation of 2 g / h between the actual value and the target value, while for higher NO _x raw emissions it corresponds to a deviation corresponds to 20%.

43. The method according to any one of the preceding claims, characterized in that after detection of an irregularity in the catalyst activity, at least one advanced NO _x regeneration is carried out.

44. The method according to claim 43, characterized in that in addition at least a de-sulfation is carried out and thereafter a catalyst defect is signaled if the irregularity persists.

45. The method of claim 43 or 44, characterized in that the number of of an advanced NOx regeneration carried out regular NO _x - determined regenerations and successive to a predetermined minimum number of NO _x is compared -Regenerationen and that upon the occurrence of a renewed irregularity in catalyst activity a catalyst defect is signaled before this minimum number is reached.

46. The method according to claim 45, characterized in that the minimum number of successive regular NO _x regeneration is 10-100.

47. The method according to claim 46, characterized in that the minimum number of successive regular NO _x regenerations is 20.

48. Common rail diesel engine (10), characterized in that a throttle valve (14) is arranged for NOx regeneration of a downstream NO _x storage catalytic converter (24) according to one of the preceding claims in front of the intake manifold.

49. Method for favoring the NO _x storage in a NOx storage catalytic converter (24) connected downstream of a lean-operated internal combustion engine (10) by measures that increase the exhaust gas temperature and / or reduce the mass flow.

50. The method according to claim 49, characterized in that the exhaust gas temperature increasing and / or mass flow reducing measures include an EGR change and / or a throttling of the fresh air quantity by up to 70% and / or a boost pressure reduction up to the pure suction operation.

51. The method according to claim 49 or 50, characterized in that the exhaust gas temperature upstream of the NO _x storage catalyst (24) is increased to a value of more than 190 ° C by the exhaust gas temperature-increasing measures.

52. Method for reducing nitrogen oxide in the exhaust gas of a lean-burn internal combustion engine (10) with a downstream NO _x storage catalytic converter (24)

Control of the NO _x regeneration of the NO _x storage catalytic converter (24) according to at least one of claims 1 - 47 and Favoring the NO _x storage according to at least one of claims 49 51.